Nearly 25 years since the discovery of the etiologic agent of AIDS, the HIV pandemic continues to be a major public health concern. As there is currently no available vaccine for HIV-1, much emphasis has been placed on the development of diagnostic tests to assist in the evaluation of various intervention strategies. Additionally, diagnosis of acute HIV-1 infection may have important implications for reducing the dissemination of the virus. During acute HIV infection, infected individuals are at a higher risk for transmitting the virus due to peak viral levels in blood, oral fluid and genital secretions prior to the development of an HIV-specific immune response (Pilcher et al., 2001). Though identification of early infection and intervention with antiretroviral therapy or risk-reduction counseling may reduce HIV transmission, only a very small percentage of acutely infected individuals are diagnosed within the first month of infection (Patel et al., 2006; Pilcher et al., 2004) or within the first 6 months following infection (Puchhammer-Stockl et al., 2005; Schacker et al., 1996).
The importance of diagnostic HIV tests in controlling the HIV epidemic is evidenced by the numerous tests currently licensed by the FDA, each having their own strengths and weaknesses (Ketema et al., 2005). Despite the evolving array of HIV diagnostic tests available, HIV testing algorithms have not been updated since the late 80's. Based on the previous CDC/ASTPHLD (Association of State and Territorial Public Health Laboratory Directors) guidelines, HIV testing in large patient populations frequently involves some combination of antibody-based enzyme immunoassay (EIA) test, followed by confirmation by Western Blot or indirect immunofluorescence assay (IFA) (1989).
The use of rapid HIV tests is highly attractive for screening of patient samples, especially in developing countries where resources are limited, because they are quick, easy to perform, and do not require any special equipment. Rapid tests for the identification of HIV antibody, however, will remain negative during the 4-5 week window post-infection and pre-seroconversion, necessitating the need for diagnosis based on p24 antigen or HIV-1 nucleic acid (Fiebig et al., 2003; Fiscus et al., 2007). HIV p24 antigen based tests are attractive for diagnosis of acute infection pre-seroconversion given that p24 antigen can be detected as early as 2 weeks post-infection (Weber, 2006). Due to the short window of peak viremia, antigen-based tests are relatively insensitive and are rarely used as primary screening tests for HIV (Iweala, 2004). For this reason, the EIA remains the “gold standard” for rapid, large-scale screening of clinical samples.
While the EIA is highly sensitive and relatively inexpensive, nucleic acid-based detection methods, such as PCR and RT-PCR, yield a positive result earlier in infection (Daar et al., 2001). With most HIV RNA detection assays, virus in plasma can be detected about 7 days prior to p24 antigen and about 12 days prior to antibody detection tests (Fiebig et al., 2003). Current PCR techniques, however, are not feasible screening approaches for developing countries or point-of-care testing due to personnel training requirements and the timely and expensive procedure, requiring sample processing, nucleic acid isolation, and multiple amplification steps. Furthermore, as compared to the EIA, HIV RNA assays are less specific, yielding as high as 1% false-positive rates (Hecht et al., 2002; Pilcher et al., 2004).
Thus, there is a continuing need for a rapid, cost-effective diagnostic test for the detection of early HIV infection, especially for use in resource-poor or point-of-care settings.